Peptide Bonds & Protein Structure - P2
Chemical structure of the peptide bond (bottom) and the three-dimensional structure of a peptide bond between an alanine and an adjacent amino acid (top/inset).
A peptide bond (circled) between Leu and Thr in a protein structure. Green=carbon, red=oxygen, blue=nitrogen. 
Protein Structure and Function
Structure of a protein is directly related to its function, so that anything that severely disrupts the shape will also disrupt the function. Denaturation is alteration of a protein shape through some form of external stress (for example, by applying heat, acid or alkali), in such a way that it can’t carry out its cellular function.

Levels of Protein Structure
Every protein has at least three levels of structure: primary, secondary and tertiary. Quaternary structure is a grouping of more than one amino acid chain.
Levels of Protein Structure: Primary, Secondary, Tertiary & Quaternary
Peptide Bonds
Peptide bonds are the covalent bonds which link amino acids together into chains, like the beads on a necklace. A dipeptide is composed of 2 amino acids linked together, a polypeptide is more than two.

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Endomembrane System of a Eukaryotic Cell, Mariana Ruiz
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FREE Printable 
Organic Macromolecule
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See the 
Organic Chemistry Lecture PPT for info that will help you complete this table.

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  • ​Primary Structure: Amino acids linked together by peptide bonds into a peptide chains.

  • Secondary Structure: Ionic bonds, hydrogen bonds, and hydrophilic / hydrophobic characteristics cause many polypeptide chains to fold into coils (α–helices), or accordion-like structures (β-pleated sheets). Proteins are typically composed of both α–helices and β-pleated sheets linked by short sequences of amino acids.

  • Tertiary Structure: This is the three-dimensional structure of single protein molecule; a spatial arrangement of secondary structures.

  • Quaternary Structure: This level of structure represents a complex of several protein molecules or polypeptide chains, which function as part of the protein complex.

Sources and Helpful Organic Chemistry Links
  • Bauman, R. (2014) Microbiology
  • Park Talaro, K. (2008) Foundations in Microbiology, McGraw-Hill.